Steroid hormone synthesis in adrenocortical cells is regulated by adrenocortiocotropin (ACTH) via activation of the cAMP-dependent protein kinase (PKA) pathway. In addition, accumulating evidence indicates that PKC is also an important regulator of steroidogenesis in adrenocortical and other steroidogenic cells. We have previously shown that PKC alpha functions as a tonic suppressor of steroidogenesis by inhibiting expression of the steroid synthetic enzymes, including the cholesterol side chain cleavage enzyme (SCC), the rate limiting enzyme for steroid synthesis. The overall goal of this proposal is to understand how PKC alpha suppresses steroidogenesis and sterid hydroxylase gene expression. These questions have been largely unexplored due to lack of an appropriate model. We have recently developed stable mouse Y1 adrenocortical cells lines in which we can acutely over-express PKC alpha (Y1alphaS), or deplete endogenous PKCalpha (Y1alphaAS). Acute activation of PKC alpha in the Y1 alpha S cell lines suppresses transcription of the SCC promoter 10 fold, indicating that PKC alpha inhibits SCC gene expression at the point of transcription. Our hypothesis that PKC alpha suppresses SCC transcription by modulating the interaction of a specific transcription factor at a cis-acting element is the promoter of this gene. The Y1alphaS and Y1alpha AS cell lines will be used to test our hypothesis as follows: In AIM 1, we will ask if PKC suppresses transcription through a cis-acting element in the SCC promoter. In AIM 2, we will use the Y1alphaS and Y1alphaS cell lines to explore the mechanism of PKC alpha suppression by identifying signal transduction pathways which function downstream of PKC to regulate SCC transcription. In AIM 3, we will ask if cross- talk between the PKC and protein kinase A (PKA) pathways moluates the level of steroidogenesis and steroid hydroxylase gene expression in adrenocortical cells. Since PKC regulates gene transcription and differentiated cell function sin a variety of cell types.